Fifty years ago this month, Lee Harvey Oswald set out to make history.

Conspiracy theorists say Oswald was used by the mob and that the plan to kill President John F. Kennedy had been long thought-out. But according to historian James Swanson: “He didn’t have a plan. He wasn’t stalking Kennedy. Fate brought them together.”

Swanson, a legal scholar at Heritage and bestselling author of “Manhunt: The 12-Day Chase for Lincoln’s Killer,” is out with a new book, “End of Days: The Assassination of John F. Kennedy.” He spoke about it at a Heritage event last week.

Swanson explained how he came to write about two Presidents who were killed in office.

“I was born on Lincoln’s birthday and developed a lifelong, really obsession with Abraham Lincoln,” he said. “I wrote the book ‘Manhunt’ because it was the book that no one had ever written that I always wanted to read.”

He continued, “After writing these books about the 19th century and Lincoln, I decided that I wanted to write a book about something that actually happened in my lifetime.”

Swanson said he approached the book about Kennedy differently than his earlier work on Lincoln, primarily because he was able to talk to eyewitnesses and people who knew the Kennedys. His research led him to the conclusion that three shots were fired, and those shots came from the Texas School Book Depository where Oswald was employed.

He explained:

Three of Oswald’s co-workers were sitting in the fifth floor windows directly below Oswald’s window. They heard: boom, boom, boom. They heard the rifle belt open and eject a cartridge and close three times. They heard those three brass cartridge cases bounce on the wooden floor above their heads. One of them said, ‘Man, somebody’s shootin’ right above our heads.’ The windows were shaking, plaster fell through the cracks of the wooden floor and fell down on them.

In addition to the three men in the room below Oswald, Swanson said that “most of the witnesses at Dealey Plaza heard three shots. People in the car, Secret Service trail car, all turned around to look at the Book Depository.”

Swanson said he tried to break down the scene into second-by-second accounts. But he said that the inclusion of the First Lady Jackie Kennedy’s side of the story is something that makes his book interesting and is a unique characteristic that many authors before him disregarded.

Jackie Kennedy did not want to leave her husband’s side after the assassination. Swanson said she traveled with the casket to all of its different locations until it was finally brought to its resting spot in Arlington Cemetery.

Swanson said that he tried to tell the story of the assassination in the most accurate and detailed way that he could, but one detail he could not include was Oswald’s reasons for shooting the president. To which he said, “We’ll never know why he did it.”

Swanson spoke at Heritage on November 6. Video of his speech, including an introduction from former Attorney General Edwin Meese, runs about 50 minutes.